distance(from:to:)' 不可用:Swift 4 中的任何字符串视图索引转换都可能失败；请打开可选索引 [英] distance(from:to:)' is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices

问题描述

我试图将我的应用程序迁移到 Swift 4、Xcode 9.我收到此错误.它来自第 3 方框架.

I was trying to migrate my app to Swift 4, Xcode 9. I get this error. Its coming from a 3rd party framework.

distance(from:to:)' 不可用:Swift 4 中的任何字符串视图索引转换都可能失败；请解开可选索引

distance(from:to:)' is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices

func nsRange(from range: Range<String.Index>) -> NSRange {
    let utf16view = self.utf16
    let from = range.lowerBound.samePosition(in: utf16view)
    let to = range.upperBound.samePosition(in: utf16view)
    return NSMakeRange(utf16view.distance(from: utf16view.startIndex, to: from), // Error: distance(from:to:)' is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices
                       utf16view.distance(from: from, to: to))// Error: distance(from:to:)' is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices
}

推荐答案

您可以像这样简单地解开可选索引:

You can simply unwrap the optional indices like this:

func nsRange(from range: Range<String.Index>) -> NSRange? {
    let utf16view = self.utf16
    if let from = range.lowerBound.samePosition(in: utf16view), let to = range.upperBound.samePosition(in: utf16view) {
       return NSMakeRange(utf16view.distance(from: utf16view.startIndex, to: from), utf16view.distance(from: from, to: to))
    }
    return nil
}

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